The present invention relates to a window sash interlock system for operating two windows in controlled fashion, and particularly to a fume hood sash interlock system for allowing operation of one sash while restricting the operation of a second sash.
When conducting experiments in a laboratory which may produce noxious vapors, gasses or dust or other irritants or harmful substances, it is common to locate these experiments within an enclosed cupboard or fume hood which is ventilated to a location exterior of the inhabited room. In practice, the fume hoods provide vertically sliding windows which can be raised to admit the laboratory technician's hands for manipulating the experiment or for placing the matter to be experimented on within the hood. It is also known that two sashes are placed side-by-side for two entryways into the hood or for two experiment stations. The sizing of sash openings is selected such that a minimum air velocity into the sash from the room during ventilation is maintained which is an important parameter to prevent infiltration of the experimental gas or other emission into the inhabited room.
Where more than one sash is provided it can be a problem that the total open sash area at any one time is greater than the design open area for minimum air velocity. That is, due to a plurality of ongoing experiments or for any other reason, more than one sash may be opened simultaneously. Because of this increased open area, the air entry velocity into the fume hood will drop to below minimum velocity and infiltration of noxious fumes or other matter into the inhabited room can occur. It is thus important to control or limit the total sash open area at any one time.
U.S. Pat. No. 4,385,551 to Zboralski and U.S. Pat. No. 4,829,887 to Holschbach disclose means where two side-by-side sashes cannot be open simultaneously due to the implementation of a flipping motion sash lock. Great Britain Patent 2,061,488 discloses a fume hood construction having four sashes with pairs connected by means of cables. Lifting or lowering of a sash affects the vertical position of a respective other sash connected thereto by the cable.
U.S. Pat. No. 3,726,206 to Worick, Jr. discloses a fume hood having three sash members connected together via a cable wrapped around a pulley, wherein movement of one sash member produces a corresponding movement of the other in an opposite direction, each sash member serving as a counterbalance for the other.
Canadian Patents 1,174,103 and 1,174,105 disclose horizontal sliding sash panels and dampers which are arranged to provide proper opening for auxiliary air. U.S. Pat. No. 3,934,496 to Turko discloses a counterbalance arrangement for a fume hood. U.S. Pat. No. 3,025,780 to Russel discloses side-by-side sashes for a laboratory fume hood wherein each sash is counterbalanced by a single counterweight connected to the respective sash by two cords.